Professional cycling has been plagued by head injuries this season, and during the Tour de France no fewer than three riders have suffered concussions in just one week of racing: Tom Boonen (Quickstep) and Janez Brajkovic (RadioShack) have dropped out of the race, while it is still to be determined if Chris Horner will continue after finishing stage 7 in a daze.

The latest spate of traumatic brain injuries (TBI) - the medical term for a concussion - and the fact that both Horner and Boonen soldiered on despite being obviously affected in terms of cognitive ability, has raised the issue of who should be the one to determine whether a rider can keep racing after landing on his head.

In Brajkovic's case, it was a broken collarbone that ended his Tour, as in all likelihood he would have climbed back on his bike with his head gushing blood if he could have: it's the mentality of a bike racer in the sport's biggest event. Nobody wants to abandon the Tour de France.

Boonen's directeur sportif left the decision on whether to continue on the rider himself after other riders complained that the Belgian was a danger to the peloton. Horner was allowed to ride to the finish in the presence of the race doctor, but he had no recollection of the crash or how long he had been chasing.

The sport has been reeling from the tragic consequences of high-speed crashes and head injuries following the death of Belgian Wouter Weylandt in the Giro d'Italia. His head trauma caused instant death, but a subsequent crash by Juan Mauricio Soler left the Movistar still unable to communicate following a medically-induced coma because of a TBI.

Cyclingnews spoke with Garmin-Cervélo physician Prentice Steffen, who questioned the idea that an affected athlete should be the one to evaluate whether he is fit to continue competing, because even if a rider can stand up and climb back on his bike it doesn't mean he is well enough to keep going.

"I think the race doctors should be the ones with the authority to make these decisions," Steffen said, but in his team's case, it is the staff who are tasked with making that difficult call.

Riders who continue to compete with TBI's not only risk causing themselves or others to crash due to reduced attention, but they also slow the healing progress by raising their heart rates and risk permanent damage should they crash again.

Steffen, who has worked in emergency medicine, came up with his own protocol for evaluating head injuries based on a repor from a conference on concussions in sport in Zurich a few years ago. The team's main lead-out man Julian Dean suffered a delayed reaction to a knock he took to the head in the Volta a Catalunya this year, and ever since then the team has carried a step-by-step guide to assessing head injuries.

"I came up with it based on research and the Zurich conference on head injuries in sport," Steffen said. At the conference, the attendees came up with a consensus for evaluating head injuries with a protocol called "SCAT2", which improved upon an earlier version of the "Standardized Assessement of Concussions" (SAC) of 2005.

The team has laminated copies of the questionnaire, modified by Steffen to be cycling-specific, inside each team car, and all staff have been trained on using it to check a rider's well being after a crash in case the team doctors aren't on hand at the accident.

The team's policy states, "Even in the absence of obvious injury to the head or damage to the helmet, the rider will then be questioned for signs of confusion, memory loss, loss of consciousness, imbalance, or any other behaviours that indicate the rider is not at his/her normal baseline mental functioning."

Of course, a rider wants to return as quickly as possible to the race if he is able, so the team can carry out the checks during the chase back to the peloton or after the rider rejoins, but if the rider shows any sign of a significant head injury, the team's policy is to remove the rider from the race immediately.

That clearly wasn't the case for Boonen, who despite having headaches and vomiting - two major signs of a serious concussion - was allowed to start the race by his team.

Horner would surely have failed at least one of the SCAT2 questions, as his team stated in a press release that he "remained foggy about his surroundings and the events of the day several hours after the stage ended". Video showed him coming across the line saying he didn't understand why he was 12 minutes behind - he had no recollection of the crash.

TBI symptoms can be as mild as an annoying headache, or more serious including confusion, dizziness, vomiting, sensitivity to light and sound or balance problems. Symptoms that may emerge later include insidious issues such as anhedonia - an absence of emotions, loss of memory, difficulty concentrating, loss of senses like taste or smell or problems controlling emotions and rage.

"Most head injuries are evident in the first hour after an accident," Steffen said, but the symptoms of a more serious problem may not show up right away. In Dean's case, swelling on the brain didn't start to cause problems until he was at the airport heading home from Catalunya.

Steffen's protocol dictates that riders are not to be left alone for six hours following the end of the race, because of possible complications like the intracranial hemorrhage which ended American Saul Raisin's career in 2006. Riders with head injuries are also prohibited from flying for three days because rapid changes in atmospheric pressure can affect the blood flow in injured parts of the brain, Steffen said.

He added that after a blow to the head, the medical staff are in charge of a rider's return to training - evaluating progress at every step, beginning with very low-level activities like a 20 minute stroll followed by checks for symptoms and only allowing for gradually increased efforts after the rider is symptom-free.

Cycling has only begun to treat head injuries as seriously as they need to, and Steffen hopes that more teams will adopt some method for evaluating riders. He once headed up the American Association of Cycling Team Doctors, but the task became too time consuming. Luckily, another group has created the Medicine of Cycling Conference, which will take place in August in Colorado. There will be a panel discussion on concussions at the event.